We are purifying and characterizing photoreactivating enzymes from procaryotes (E. coli) and eucaryotes (human placenta, Thermobia domestica, orchid, Drosophila). We are studying the substrate range, specificity, wavelength dependence and mechanism of action of these enzymes. We are also investigating the function of the photoreactivating enzyme in repair of pyrimidine dimers in cellular DNA of cultured cells, human leukocytes and human skin. We have developed a system for UV induction of transformation to anchorage-independent growth in human cells. We are investigating the properties of the transformants and the role of DNA repair processes in preventing or enhancing the transformation process.